A network called a “body area network” is known as a wireless network formed around a human body. In the body area network, a hub as a central device and nodes as terminal devices are attached to the human body and communication is performed between the hub and nodes.
IEEE802.15.6 discloses an access scheme using one channel as an example of a communication method between the hub and nodes in the body area network. On the other hand, unlike such a scheme, a mechanism is also under study in which the hub uses a control channel and a data channel. More specifically, a method is under study whereby when it is desirable to change a data channel to another data channel for a reason that the data channel is affected by interference or the like, the node temporarily returns to the control channel to identify the changed data channel using a beacon signal of the control channel. According to this method, when the data channel is changed, the node need not perform a channel search on all data channel candidates and can thereby possibly reduce power consumption. The hub receives a beacon signal of the control channel from another hub, and can thereby acquire information on the data channel or the like used in the other hub. In this case, to prevent power consumption from increasing due to an increase of channel search, it is preferable to set a smaller number of candidates for the control channel than for the data channel.
On the other hand, as another technique, when a channel currently in use is changed to another channel, a mechanism of searching channels different from the operating channel is being reviewed. For example, a mechanism is being proposed as application for sensor communication in which while being connected to a terminal device, for such a short period of time that a retransmitted signal from the terminal device can be received, reception processing of a channel in use is suspended and a search is performed to determine whether another cannel is busy or not.
However, according to the technique, since the channel suspension period is short, it is all right when handling an emergency signal which becomes a problem in the body area network, but the technique spends a short time searching for other channels. If this prior art is applied to a body area network, the problem is that the search time is too short for the hub to switch the data channel to the control channel, receive a beacon signal of the other hub and obtain information on the data channel.